Drive circuit for semiconductor switching element and semiconductor switching element module having the same

ABSTRACT

In a drive circuit, a threshold voltage control device is activated when a mode determination circuit determines a specific mode switching signal. The threshold voltage control device controls a threshold voltage of a comparator through a threshold voltage setting device to be sequentially changed in a period where a semiconductor switching element is turned on in a state where a constant current is externally supplied between conduction terminals of the semiconductor switching element. The threshold voltage control device stores data corresponding to the threshold voltage of a time point where an output signal of the comparator changes due to the threshold voltage being changed to a nonvolatile storage. The threshold voltage control device reads out the threshold voltage from the storage and permits the threshold voltage setting device to set the threshold voltage read out to the comparator, when the mode determination circuit determines a drive control signal.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2014-159447filed on Aug. 5, 2014, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a drive circuit that provides a drivesignal to a conduction control terminal of a semiconductor switchingelement according to a drive control signal received from an externaldevice, and a semiconductor switching element module having the drivecircuit and the semiconductor switching element.

BACKGROUND

For example, in order to detect a current flowing through asemiconductor switching element, such as an insulated gate bipolartransistor (IGBT), it has been known to use an element having a mainIGBT and a sensing IGBT for detecting the current. In general, the ratioof the current flowing in the main IGBT and the current flowing in thesensing IGBT largely varies. If the current detected by the sensing IGBTis directly used, a detection value also largely varies.

When an overcurrent protection of the main IGBT is carried out based onsuch a current largely varying, it is necessary to estimate the worstvalue of the current to a larger value. The element size of the IGBTneeds to be selected to have a margin to breakdown according to theworst value. For example, JP 2013-198185 A, which corresponds to US2013/0242438 A1, discloses an example of a structure for detectingovercurrent in a switching element.

SUMMARY

For example, there is a method of correcting an overcurrent detectionthreshold set to a drive circuit according to a current value actuallydetected in each IGBT. In this case, however, it is necessary to controleach IGBT and the drive circuit connected to each IGBT to have arelationship, and thus the control is complicated. Further, if therelationship between the IGBT and the drive circuit is erroneously made,it is difficult to correct the erroneous relationship later. Moreover, ameasuring environment at the time of obtaining data and an operatingenvironment when in use as a product may be different. Furthermore, thedrive circuit may have variations in characteristics, and parasiticcomponents due to the structure when the IGBT and the drive circuit areintegrated as a module may occur. Such difference of the environments,the variation in the characteristics of the drive circuit, and theparasitic components may cause errors.

It is an object of the present disclosure to provide a drive circuit fora semiconductor switching element, which is capable of adjusting athreshold for suitably detecting overcurrent in a semiconductorswitching element according to characteristics of an individualsemiconductor switching element. It is another object of the presentdisclosure to provide a semiconductor switching module including thedrive circuit and the semiconductor switching element.

According to a first aspect of the present disclosure, a drive circuitis for providing a drive signal to a conduction control terminal of asemiconductor switching element according to a drive control signalreceived from an external device through an input terminal. The drivecircuit includes a comparator, a threshold voltage setting device, anonvolatile storage, a mode determination circuit, and a thresholdvoltage control device. The comparator compares a voltage convertedaccording to a current generated when the semiconductor switchingelement is turned on with a threshold voltage, and outputs anovercurrent detection signal. The threshold voltage setting devicevariably sets the threshold voltage. The nonvolatile storage stores datacorresponding to the threshold voltage. The mode determination circuitdetermines whether an input signal received from the external devicethrough the input terminal is the drive control signal or a specificmode switching signal. The threshold voltage control device is activatedwhen the mode determination circuit determines that the input signal isthe specific mode switching signal. The threshold voltage control devicecontrols the threshold voltage through the threshold voltage settingdevice to be sequentially changed in a period where the semiconductorswitching element is turned on in a state where a constant current isexternally supplied between conduction terminals of the semiconductorswitching element. The threshold voltage control device stores datacorresponding to the threshold voltage of a time point where an outputsignal of the comparator changes due to the threshold voltage beingchanged in the storage. Further, the threshold voltage control devicereads out the threshold voltage based on the data stored in the storageand permits the threshold voltage setting device to set the thresholdvoltage read out to the comparator, when the mode determination circuitdetermines that the input signal is the drive control signal.

In such a structure, when the mode switching signal is inputted in thestate where the constant current can be supplied between the conductionterminals of the semiconductor switching element, the threshold voltagecontrol device automatically determines a suitable threshold voltageaccording to the characteristics of the semiconductor switching element,and stores the threshold voltage determined to the storage. When thedrive control signal is inputted, the threshold voltage control devicereads out the threshold voltage from the storage and sets the thresholdvoltage to the comparator. Therefore, the threshold voltage for theovercurrent detection can be suitably set according to thecharacteristics of the semiconductor switching element actually used oran operating environment thereof.

According to a second aspect of the present disclosure, a drive circuitis for providing a drive signal to a conduction control terminal of asemiconductor switching element according to a drive control signalreceived from an external device through an input terminal. The drivecircuit includes an A/D converter, a comparator, a nonvolatile storage,and a mode determination circuit. The A/D converter converts a voltagethat has been converted according to a current generated when thesemiconductor switching element is turned on into a digital data. Thecomparator compares the digital data with a threshold data, and outputsan overcurrent detection signal. The nonvolatile storage stores thethreshold data. The mode determination circuit determines whether aninput signal received from the external device through the inputterminal is the drive control signal or a specific mode switchingsignal. When the mode determination circuit determines that the inputsignal is the specific mode switching signal, the storage stores thedigital data converted through the A/D converter in a period where thesemiconductor switching element is turned on in a state where a constantcurrent is externally supplied between conduction terminals of thesemiconductor switching element. When the input signal is the drivecontrol signal, the comparator compares the digital data converted bythe A/D converter and the threshold data stored in the storage.

In such a structure, when the mode switching signal is inputted in thestate where the constant current can be supplied between the conductionterminals of the semiconductor switching element, a suitable thresholdvoltage according to the characteristics of the semiconductor switchingelement is automatically determined and stored in the storage. When thedrive control signal is inputted, the threshold voltage stored in thestorage is set to the comparator. Therefore, the threshold voltage forthe overcurrent detection can be suitably set according to thecharacteristics of the semiconductor switching element actually used oran operating environment thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings, in whichlike parts are designated by like reference numbers and in which:

FIG. 1 is a schematic block diagram of an IGBT module according to afirst embodiment of the present disclosure;

FIG. 2A is a schematic block diagram of the IGBT module in a state wherea scanning circuit performs a scanning operation;

FIG. 2B is a diagram illustrating a time chart in the scanningoperation;

FIG. 3A is a waveform chart of a normal gate signal according to thefirst embodiment;

FIG. 3B is a waveform chart of an example of a mode switching signalaccording to the first embodiment;

FIG. 3C is a waveform chart of another example of the mode switchingsignal according to the first embodiment;

FIG. 4A is a schematic block diagram of a mode determination circuit ofthe IGBT module according to the first embodiment;

FIG. 4B is a diagram illustrating an internal clock signal and datapatterns of the mode switching signal according to the first embodiment;

FIG. 5 is a flowchart illustrating a process including a scanningoperation according to the first embodiment;

FIG. 6 is a schematic block diagram of an IGBT module according to asecond embodiment of the present disclosure;

FIG. 7 is a time chart illustrating a writing high voltage applied to aninput terminal of the IGBT module and an operation of a switch accordingto the second embodiment;

FIG. 8 is a schematic block diagram of an IGBT module according to athird embodiment of the present disclosure;

FIG. 9 is a flowchart illustrating a process including a scanningoperation according to the third embodiment;

FIG. 10 is a schematic block diagram of an IGBT module according to afourth embodiment of the present disclosure; and

FIG. 11 is a flowchart illustrating a process of a threshold dataaccording to the fourth embodiment.

DETAILED DESCRIPTION First Embodiment

As shown in FIG. 1, an IGBT module 1 of the present embodiment is amodule into which an IGBT 2 as a semiconductor switching element and adriver IC 3 as a drive circuit are integrated. A collector and anemitter of the IGBT 2 are respectively connected to external terminals Cand E of the IGBT module 1. The IGBT 2 includes a sensing IGBT forsensing an electric current. An emitter of the sensing IGBT is connectedto the external terminal E through a resistive element 4. The externalterminal E is also connected to an external terminal GND inside of theIGBT module 1.

A gate control signal outputted from a microcomputer (MC) as a controldevice or an example of an external device is provided to an externalterminal IN through a photo-coupler (CP) 5. Ends of a secondary windingof a transformer 6 are respectively connected to the external terminalsVB and GND. A power supply voltage VB, which has been transformed basedon a power supply (not shown) connected to a primary winding of thetransformer 6, is supplied between the external terminal VB and theexternal terminal GND.

A gate drive circuit 7 is supplied with the power supply voltage VB. Thegate drive circuit 7 receives the gate control signal through theterminal IN. The gate drive circuit 7 provides a gate drive signal tothe gate of the IGBT 2. The gate control signal is also provided to amode determination circuit 8. The mode determination circuit 8determines whether the signal provided is a normal gate control signalor a mode switching signal that indicates a pattern different from thatof the normal gate control signal. When determining that the signalprovided is the mode switching signal, the mode determination circuit 8activates a scanning circuit 9. The scanning circuit 9 corresponds to athreshold voltage control device.

A non-inverting input terminal of a comparator 10 is connected to theemitter of the sensing IGBT. An inverting input terminal of thecomparator 10 is applied with a threshold voltage VT outputted from a VTconversion circuit 11. The VT conversion circuit 11 corresponds to athreshold voltage setting device. The VT transform circuit 11 is, forexample, provided by a digital-to-analog (D/A) converter. The VTconversion circuit 11 outputs an analog voltage according to dataprovided from the scanning circuit 9, as the threshold voltage VT. Anoutput of the comparator 10 is provided to the gate drive circuit 7 andthe scanning circuit 9.

A memory (M) 12 is a non-volatile memory, such as EEPROM or a flashmemory. Data can be written into or read out from the memory 12 by thescanning circuit 9. The memory 12 corresponds to a storage. The memory12 can be selectively supplied with the power supply voltage VB or acontrol power supply voltage VC for reading out the data by means of aswitch 13. The scanning circuit 19 controls the switching operation ofthe switch 13. The scanning circuit 19 controls the switch 13 so thatthe power supply voltage VB is supplied to the memory 12 when the datais written in the memory 12.

The driver IC 3 automatically obtains and sets an optimal value of thethreshold voltage VT to the comparator 10 for overcurrent determinationof the IGBT 2 as an object to drive. In such a case, as shown in FIG.2A, a current source that generates a constant current I1 correspondingto a value that is determined as the overcurrent is connected beforehandbetween the external terminal C and the external terminal E of the IGBTmodule 1. As shown in FIG. 2B, after providing the mode switching signalto the terminal IN, the microcomputer provides the gate control signalbeing at a high level to the terminal IN to make the IGBT 2 in an onstate. As a result, a collector current of the IGBT 2 begins toincrease, and a terminal voltage SOC of the resistive element 4 alsoincreases. In this state, the scanning circuit 9 is activated. Theoperation of the scanning circuit 9 will be described later in detail.

The mode switching signal is provided as a signal having a pattern thatchanges differently from the pattern of the normal gate control signal(PWM signal) shown in FIG. 3A. For example, the mode switching signalhas an irregular cyclic pattern, differently from the carrier wave forthe PWM control having a constant cycle, as shown by an example 1 ofFIG. 3B. As another example, the mode switching signal has an irregularvoltage amplitude, differently from the carrier wave for the PWM controlhaving a constant voltage amplitude, as shown by an example 2 of FIG.3C. In this case, the mode switching signal may have a pattern in whichthe amplitude exceeds a contact threshold voltage VT1 shown by a dashedline in FIG. 3C.

As shown in FIG. 4A, the mode determination circuit 8 includes asynchronous circuit 14, a register 15, and a determination portion 16.The synchronous circuit 14 receives the signal provided to the terminalIN and an internal clock signal CLK. The internal clock signal CLK has afrequency equal to or greater than twice the frequency of the PWMsignal. The internal clock signal CLK is applied to a terminal CLK ofthe register 15 in a state of synchronizing with the signal provided tothe terminal IN by means of the synchronous circuit 14.

A terminal DATA of the register 15 receives the signal provided to theterminal IN. In this example, the signal provided to the terminal IN isthe mode switching signal having the irregular cyclic pattern shown inFIG. 3B. The signal has a data pattern of 11 bits indicating“01110101110” when reading at rising edges of the internal clock signalCLK. When this data is stored in the register 15, the determinationportion 16 compares this data with a data pattern of the mode switchingsignal that is set beforehand. When the data coincides with the datapattern of the mode switching signal set beforehand, the determinationportion 16 determines to switch the mode. Thus, the mode determinationcircuit 8 activates the scanning circuit 9.

Next, an operation of the present embodiment will be described. As shownin FIG. 5, the driver circuit IC 3 is supplied with the electric powerat S1. The driver circuit IC 3 is in a state of waiting for the signalinputted to the terminal IN (IN signal) from the microcomputer at S2.When the microcomputer outputs the IN signal at M1, the modedetermination circuit 8 performs a mode determination at S3. Whendetermining that the IN signal is the mode switching signal (S3: YES),the mode determination circuit 8 sets the gate of the IGBT 2 to the onlevel according to the gate control signal subsequently provided fromthe microcomputer at S4. Then, the scanning circuit 9 is activated tostart a scanning operation of the threshold voltage VT at S5.

The scanning circuit 9 provides an initial value at first. At S6, thescanning circuit 9 changes the data of the threshold voltage VT inputtedto the VT conversion circuit 11, and the VT conversion circuit 11provides the analog threshold voltage VT to the inverting input terminalof the comparator 10 according to the data received. At S7, the scanningcircuit 9 compares the change of the signal outputted from thecomparator 10.

The initial value of the threshold voltage VT is set to a lower value.Since the IGBT 2 is turned on at S5, the collector current of the IGBT 2is the constant current I1, and the terminal voltage of the resistiveelement 4 has a value corresponding to the current having apredetermined ratio to the constant current I1. As shown in FIG. 2B,therefore, the output signal of the comparator 10 indicates the highlevel at first.

In a period where the output signal of the comparator 10 is at the highlevel (S7: NO), the process returns to S6 and the scanning circuit 9sequentially increases the threshold voltage VT. When the output signalof the comparator 10 changes from the high level to the low level (S7:YES), the scanning circuit 9 stops the scanning operation at S8. This isbecause the threshold voltage VT applied to the comparator 10 at thetime point where the output signal changes from the high level to thelow level is the value appropriate as the threshold for detecting theovercurrent. Therefore, in the normal operation, when the collectorcurrent, which is generated according to the switching operation of theIGBT 2, exceeds the current value I1, the output signal of thecomparator 10 changes from the low level to the high level. As a result,the overcurrent is detected. In this case, the output signal of thecomparator 10 changing from the low level to the high level correspondsto the output of the overcurrent detection signal.

When the overcurrent is detected, the gate drive circuit 7 keeps theIGBT 2 in the off state. During the scanning operation described above,the IGBT 2 needs to be kept in the on state even when the output signalof the comparator 10 is at the high level (see FIG. 2B). Therefore, themode determination circuit 8 provides a signal for invalidating theovercurrent detection to the gate drive circuit 7. Next, the scanningcircuit 9 writes data corresponding to the threshold voltage VT to thememory 12 to be stored at S9 and S10. Then, the process returns to S3.

When the IN signal is not the mode switching signal at S3 (S3: NO), themode determination circuit 8 determines whether the threshold voltage VThas been set or not referring to a flag, which will be described later,at S11. When the threshold voltage VT has not been set (S11: NO), thescanning circuit 9 reads out the data corresponding to the thresholdvoltage VT stored in the memory 12 at S12, and sets the thresholdvoltage VT to the VT conversion circuit 11 at S13. When a flagindicating that the threshold voltage VT has been set is set at S14, thenormal operation of the IGBT 2, that is, the switching control of theIGBT 2 according to the PWM signal is performed at S15. When it isdetermined that the threshold voltage VT has been set (S11: YES), theprocess proceeds to S15.

As described above, in the present embodiment, the driver IC 3 includesthe VT conversion circuit 11 for setting the threshold voltage VT to bevariable to the comparator 10 that outputs the overcurrent detectionsignal, and the memory 12 for storing the threshold voltage. The modedetermination circuit 8 determines whether the signal inputted to theinput terminal IN from an external device is the gate control signal orthe specific mode switching signal.

The scanning circuit 9 is activated when the mode determination circuit8 determines the mode switching signal being inputted. The scanningcircuit 9 sets the threshold voltage VT to sequentially change throughthe VT conversion circuit 11 in the period where the IGBT 2 is in the onstate in the state where the constant current I1 is externally suppliedbetween the collector and the emitter.

When the output signal of the comparator 10 changes from the high levelto the low level according to the change of the threshold voltage VT,the scanning circuit 9 stores the threshold voltage VT of the time pointwhere the output signal of the comparator 10 changes from the high levelto the low level in the memory 12. Thereafter, when the modedetermination circuit 8 determines that the drive control signal isinputted, the scanning circuit 9 reads out the threshold voltage storedin the memory 12, and sets the threshold voltage read out to thecomparator 10 through the VT conversion circuit 11. Therefore, thethreshold voltage VT for the overcurrent detection can be properly setaccording to characteristics of the IGBT 2 actually used or an operatingenvironment when the IGBT 2 is operated.

In the case where the mode switching signal has the frequency differentfrom the frequency of the carrier wave of the PWM signal, the modedetermination circuit 8 detects the change (difference) of thefrequency. That is, the mode determination circuit 8 determines whetherthe signal has the specific data pattern. Therefore, the determinationof the input of the mode switching signal is easily performed. In thecase where the mode switching signal has the amplitude different fromthe amplitude of the PWM signal, the mode determination circuit 8performs the determination by detecting the change (difference) of theamplitude, that is, by determining whether the amplitude exceeds thethreshold voltage VT1. Also in this case, the determination of the inputof the mode switching signal is easily performed.

Second Embodiment

Hereinafter, components same or similar to those of the first embodimentwill be designated with the same reference numbers, and descriptionsthereof will not be repeated. Hereinafter, components different from thefirst embodiment will be mainly described.

An IGBT module 21 of the second embodiment is supplied with the voltagefor writing data (data-writing voltage) to the memory 12 of a driver IC22 from the input terminal IN. Therefore, the driver IC 22 includes acomparator 23 for controlling the switch 13. In this case, the switch 13corresponds to a selector, and the comparator 23 corresponds to avoltage switching control device. A non-inverting input terminal of thecomparator 23 is connected to the input terminal IN, and an invertinginput terminal of the comparator 23 is applied with a threshold voltageVT2. In FIG. 6, the illustration of the current source I1 is omitted.

A data-writing high voltage supplied to the memory 12 is higher than thethreshold voltage VT2. As shown in FIG. 7, when the data-writing voltageV_(WH) is applied to the input terminal IN from an external device in aperiod where a scanning circuit 9A is performing the scanning operation(the IGBT 2 is kept in the on state), the output signal of thecomparator 23 changes from the low level to the high level. Thus, thedata-writing high voltage V_(WH) is supplied to the memory 12. Theoutput signal of the comparator 23 is also applied to the scanningcircuit 9A. Therefore, the scanning circuit 9A writes data correspondingto the threshold voltage VT to the memory 12 in the period where thedata-writing high voltage is being supplied to the memory 12, based onthe change of the output signal as the trigger.

In the second embodiment, as described above, the driver IC 22 includesthe switch 13 to selectively input the voltage VC for the normaloperation and the data-writing voltage to the memory 12, in thestructure where the data-writing voltage for writing the data in thememory 12 is inputted to the input terminal IN. The comparator 23detects the change of the voltage applied to the input terminal IN andcontrols the switch 13. Further, the comparator 23 provides the triggerto the scanning circuit 9A to write the data corresponding to thethreshold voltage VT in the memory 12.

Third Embodiment

As shown in FIG. 8, an IGBT module 31 of a third embodiment includes adiode 32 for detecting the temperature of the IGBT 2, and a driver IC 33includes a temperature monitoring portion 34. The diode 32 correspondsto a temperature detection device. The temperature monitoring portion 34corresponds to the threshold voltage control device. An anode of thediode 32 is supplied with a constant voltage from the temperaturemonitoring portion 34. The temperature monitoring portion 34 detects thetemperature of the IGBT 2 according to the change of a forward voltageof the diode 32. An output signal of the temperature monitoring portion34 is provided to the memory 12 as a writing address. The temperaturemonitoring portion 34 assigns the writing address in regard to theforward voltage of the diode 32 every interval having some extent.

Next, an operation of the third embodiment will be described.

As shown in FIG. 9, the process includes S21 and S22, in place of S10and S12 of the first embodiment. At S21, the threshold voltage VT iswritten in the memory 12. In this case, the threshold voltage VT iswritten in an address (writing region) according to the temperature ofthe IGBT 2 detected by the diode 32 at that time. This is because thevalue of the threshold voltage VT varies according to the temperature ofthe IGBT 2. Therefore, the writing of the data at S21 is performedseveral times while changing the temperature considering an assumedtemperature in an operating environment when the IGBT module 31 isoperated.

When it is determined that the threshold voltage VT has not been set atS11 (S11: NO), the threshold voltage VT is read out from the address ofthe memory 12 corresponding to the temperature of the IGBT 2 detected atthat time at S22.

In the third embodiment, as described above, the IGBT module 31 includesthe diode 32 for detecting the temperature of the IGBT 2. When thescanning circuit 9 stores the threshold voltage VT in the memory 12, thetemperature monitoring portion 34 permits the threshold voltage VT to bestored in the storing region according to the temperature detected bythe diode 32. When the mode determination circuit 8 determines the inputof the gate control signal, the scanning circuit 9 reads out thethreshold voltage VT according to the temperature detected by the diode32 from the memory 12 and sets the threshold voltage VT to thecomparator 10. Therefore, the threshold voltage VT according to thetemperature of the operating environment of the IGBT 2 can be suitablyset to the comparator 10.

Fourth Embodiment

In an IGBT module 41 of a fourth embodiment, as shown in FIG. 10, adriver IC 42 is not provided with the scanning circuit 9, but isprovided with an A/D converter 43 and a (digital) comparator 44. Thedriver IC 42 has a memory 45, in place of the memory 12. The memory 45corresponds to the storage. An output terminal of the A/D converter 43is connected to a (+) terminal of the comparator 44, and is alsoconnected to an input terminal of the memory 45 through a switch 46.

When determining that the mode switching signal is inputted to the inputterminal IN, the mode determination circuit 8 controls the switch 46 toturn on. In the other cases, that is, when the mode switching signal isnot inputted to the input terminal IN, the mode determination circuit 8controls the switch 46 to turn off. An output terminal of the memory 45is connected to a (−) terminal of the comparator 44. The data written inthe memory 45 is always applied to the (−) terminal of the comparator44. An output terminal of the comparator 44 is connected to an inputterminal of the gate drive circuit 7.

Next, an operation of the fourth embodiment will be described. As shownin FIG. 11, after S2 is performed, an analog-to-digital (A/D) conversionis performed by the A/D converter 43 at S31. The digital data convertedat S31 is the terminal voltage when the constant current I1 is appliedto the resistive element 4, and indicates an appropriate value as thethreshold data for comparison in the comparator 44. Therefore, after S4is performed, the digital data converted by the A/D converter 43 iswritten in the memory 45 at S32.

In the normal operation, which is determined as “NO” at S3, thecomparator 44 compares the threshold data that is outputted from thememory 45 and is applied to the (−) terminal and the digital dataconverted by the A/D converter 43 at that time, thereby to detect theovercurrent, at S33.

In the fourth embodiment, as described above, the driver IC 42 includesthe A/D converter 43 for converting the voltage converted according tothe current flowing when the IGBT 2 is turned on into the digital data,and the memory 45 for storing the threshold data. When the modedetermination circuit 8 determines the input of the mode switchingsignal, the memory 45 stores the data that is converted into the digitaldata by the A/D converter 43 as the threshold data in the period wherethe IGBT 2 is in the on state as the constant current I1 is externallysupplied between the collector and the emitter.

In the state where the gate control signal is inputted to the inputterminal IN from the external device, the comparator 44 compares thedigital data converted by the A/D converter 43 and the threshold datastored in the memory 45. Therefore, similarly to the first embodiment,the threshold voltage for detecting the overcurrent can be suitably setaccording to the characteristics of the IGBT 2 actually used or theoperating environment when in use. Further, the control process isfurther simplified, as compared with that of the first embodiment.

The present disclosure is not limited to the embodiments describedhereinabove and illustrated in the drawings, but may be modified orextended as follows.

For example, the structure of the second embodiment and the structure ofthe fourth embodiment may be combined together.

The temperature detection device is not limited to the diode 32, but maybe a thermistor or the like.

The storage device may include a fuse memory.

It is not always necessary that the IGBT 2 has the sensing IGBT.

In place of the resistive element 4, a current sensor may be used todetect a current and the current detected may be converted to a voltagesignal.

It is not always necessary to integrate the IGBT 2 and the driver ICinto the IGBT module. The IGBT and the driver IC may be configured asseparate devices.

The semiconductor switching element is not limited to the IGBT 2, butmay be a MOSFET or a bipolar transistor.

While only the selected exemplary embodiment and examples have beenchosen to illustrate the present disclosure, it will be apparent tothose skilled in the art from this disclosure that various changes andmodifications can be made therein without departing from the scope ofthe disclosure as defined in the appended claims. Furthermore, theforegoing description of the exemplary embodiment and examples accordingto the present disclosure is provided for illustration only, and not forthe purpose of limiting the disclosure as defined by the appended claimsand their equivalents.

What is claimed is:
 1. A drive circuit for providing a drive signal to aconduction control terminal of a semiconductor switching elementaccording to a drive control signal received from an external devicethrough an input terminal, the drive circuit comprising: a comparatorcomparing a voltage converted according to a current generated when thesemiconductor switching element is turned on with a threshold voltage,and outputting an overcurrent detection signal; a threshold voltagesetting device variably setting the threshold voltage; a nonvolatilestorage storing data corresponding to the threshold voltage; a modedetermination circuit determining whether an input signal received fromthe external device through the input terminal is the drive controlsignal or a specific mode switching signal; and a threshold voltagecontrol device: being activated when the mode determination circuitdetermines that the input signal is the specific mode switching signal;controlling the threshold voltage through the threshold voltage settingdevice to be sequentially changed in a period where the semiconductorswitching element is turned on in a state where a constant current isexternally supplied between conduction terminals of the semiconductorswitching element; storing data corresponding to the threshold voltageof a time point where an output signal of the comparator changes due tothe threshold voltage being changed in the storage; and reading out thethreshold voltage based on the data stored in the storage and permittingthe threshold voltage setting device to set the threshold voltage readout to the comparator, when the mode determination circuit determinesthat the input signal is the drive control signal.
 2. The drive circuitaccording to claim 1, further comprising: a temperature detecting devicedetecting a temperature of the semiconductor switching element, whereinthe threshold voltage control device stores the data corresponding tothe threshold voltage in a predetermined storage region of the storageaccording to the temperature detected by the temperature detectingdevice, and when the mode determination circuit determines that theinput signal is the drive control signal, the threshold voltage controldevice reads out the data corresponding to the threshold voltageaccording to the temperature detected by the temperature detectiondevice from the storage, and permits the threshold voltage read out tobe set to the comparator.
 3. The drive circuit according to claim 1,wherein the mode switching signal has a frequency different from afrequency of the drive control signal, and the mode determinationcircuit determines whether the input signal is the drive control signalor the specific mode switching element based on a change of thefrequency.
 4. The drive control circuit according to claim 1, whereinthe mode switching signal has an amplitude different from an amplitudeof the drive control signal, and the mode determination circuitdetermines whether the input signal is the drive control signal or thespecific mode switching element based on a change of the amplitude. 5.The drive control circuit according to claim 1, wherein the inputterminal receives a data-writing voltage for writing data in thestorage, the drive control circuit further including: a selectorselectively inputting a voltage for a normal operation and thedata-writing voltage in the storage; and a voltage switching controldevice controlling the selector to switch between input of the voltagefor the normal operation and input of the data-writing voltage, whereinthe voltage switching control device controls the selector to switchfrom the input of the voltage for the normal operation to the input ofthe data-writing voltage, when detecting that the input terminalreceives the data-writing voltage.
 6. A semiconductor switching elementmodule comprising: a semiconductor switching element; and the drivecircuit according to claim
 1. 7. A drive circuit for providing a drivesignal to a conduction control terminal of a semiconductor switchingelement according to a drive control signal received from an externaldevice through an input terminal, the drive circuit comprising: an A/Dconverter converting a voltage that has been converted according to acurrent generated when the semiconductor switching element is turned oninto a digital data; a comparator comparing the digital data with athreshold data, and outputting an overcurrent detection signal; anonvolatile storage storing the threshold data; and a mode determinationcircuit determining whether an input signal received from the externaldevice through the input terminal is the drive control signal or aspecific mode switching signal, wherein when the mode determinationcircuit determines that the input signal is the specific mode switchingsignal, the storage stores the digital data converted through the A/Dconverter in a period where the semiconductor switching element isturned on in a state where a constant current is externally suppliedbetween conduction terminals of the semiconductor switching element, andwhen the input signal is the drive control signal, the comparatorcompares the digital data converted by the A/D converter and thethreshold data stored in the storage.
 8. The drive circuit according toclaim 7, wherein the mode switching signal has a frequency differentfrom a frequency of the drive control signal, and the mode determinationcircuit determines whether the input signal is the drive control signalor the specific mode switching element based on a change of thefrequency.
 9. The drive control circuit according to claim 7, whereinthe mode switching signal has an amplitude different from an amplitudeof the drive control signal, and the mode determination circuitdetermines whether the input signal is the drive control signal or thespecific mode switching element based on a change of the amplitude. 10.The drive control circuit according to claim 7, wherein the inputterminal receives a data-writing voltage for writing data in thestorage, the drive control circuit further including: a selectorselectively inputting a voltage for a normal operation and thedata-writing voltage in the storage; and a voltage switching controldevice controlling the selector to switch between input of the voltagefor the normal operation and input of the data-writing voltage, whereinthe voltage switching control device controls the selector to switchfrom the input of the voltage for the normal operation to the input ofthe data-writing voltage, when detecting that the input terminalreceives the data-writing voltage.
 11. A semiconductor switching elementmodule comprising: a semiconductor switching element; and the drivecircuit according to claim 7.